A method of the kind described above is known from U.S. Pat. No. 4,945,856. In this a solid para-xylylene is brought into the form of a gas. The gas is conducted through gas lines into a pyrolysis chamber, where the dimer is decomposed into a monomer. The monomer is conducted, together with the carrier gas, through a further gas line that has a gas inlet element into a deposition chamber, where it is polymerized on a substrate which lies on a cooled susceptor. Para-xylylene copolymers are described by U.S. Pat. No. 3,288,728. These are C, N, D polymers of the family of parylenes that are in the form of a solid powder or a liquid at room temperature.
It is known from “Characterization of Parylene Deposition Process for the Passivation of Organic Light Emitting Diodes”, Korean J. Chem. Eng., 19(4), 722-727 (2002) to passivate, in particular to encapsulate, OLEDs with layers of poly-p-xylyene and derivatives thereof. Otherwise, it is known to provide various large-area substrates with a parylene coating in a vacuum. For example, glass, metal, paper, paint, plastics, ceramic, ferrite and silicone are coated with a pore-free, transparent polymer film by condensation from the gas phase. This exploits the hydrophobic, chemically resistant and electrically insulating property of the polymeric coating.
U.S. Pat. No. 5,554,220 describes a so-called OVPD process, by which so-called OLEDs (Organic Light Emitting Devices) can be produced. DAST is mentioned, inter alia, in this as a starting material.
DE 101 36 858 describes an apparatus and a method for the production of coated substrates, the layer being applied to a substrate by means of a condensation process. The substrate may be glass, a film or plastics. With the apparatus described here, light emitting components, in particular thin-film components such as OLEDs, may be produced. The organic layers are deposited in a structured way, using a mask, to a large area of the substrate. The apparatus has a temperature-controlled gas inlet element in the form of a gas distributor of large area and a susceptor for receiving a substrate, which is cooled and is located below the distributor.
EP 0 862 664 B1 relates to a method and an apparatus for the deposition of parylene on semiconductor substrates. Parylene is evaporated in an evaporation chamber. The evaporated parylene is decomposed in a pyrolysis chamber. The products of decomposition reach a process chamber through a gas inlet element and form a layer on a substrate that is cooled to below 15° C. The substrate holder may be heated up to 400° C. by means of a heater.
US 2006/0113507 A1 likewise relates to a parylene deposition process under vacuum conditions. Here, a liquid crystal polymer film is deposited in a single-step process. The process takes place in a three-zone reactor, which has a sublimation zone, a pyrolysis zone and a condensation zone with an operating temperature from 450° C. to 700° C. The sublimation is said to take place at a temperature between 15° C. and 100° C. The condensation and the simultaneous polymerization is said to take place at a temperature between 210° C. and 290° C.
U.S. Pat. No. 6,709,715 B1, U.S. Pat. No. 6,362,115 B1 and U.S. Pat. No. 5,958,510 A disclose a method for depositing parylene layers by use of an apparatus in which a polymeric starting material is first of all evaporated, is then decomposed and the decomposition products are introduced into a heated process chamber through a large-area gas distributor. Condensation takes place on substrates, which lie on a cooled susceptor.
U.S. Pat. No. 3,908,046 relates to a para-xylylene polymer deposition method, which also encompasses the process steps of sublimation, pyrolysis and deposition. Here, the substrate temperature is held in a range from 25° C. to 30° C.
The coating process for deposition of the OLEDs or the polymers takes place in a deposition chamber in which there is a vertical temperature gradient in the gas phase. The gas inlet element has a higher temperature than the substrate. The substrate has therefore to be cooled by support on the substrate. Heat transferred to the substrate from the gas inlet element by radiation must be conducted away to the susceptor. Since the coating process takes place as a rule in the presence of a pressure in the sub-mbar range, the removal of the heat can only be effected by contacting surface portions between the substrate and the supporting surface of the susceptor. It is naturally the case that for the two surfaces of the supporting surface on the one hand and the lower side of the substrate on the other hand that lie on one another, a true contact that allows heat conduction is only present sporadically. On account of the unavoidable lack of evenness of the two surfaces, intervening gap spaces are formed with gap widths of up to 100 μm. In the case of a process pressure of less than 1 mbar, there is no longer any heat transfer by convection in this gap. This results in the surface of the substrate to be coated being heated up by the radiation emitted by the heated gas inlet element to temperatures which are significantly above the temperature of the susceptor.